In the holy things of the Lord - This law seems to relate particularly to sacrilege, and defrauds in spiritual matters; such as the neglect to consecrate or redeem the firstborn, the withholding of the first-fruits, tithes, and such like; and, according to the rabbins, making any secular gain of Divine things, keeping back any part of the price of things dedicated to God, or withholding what man had vowed to pay. See a long list of these things in Ainsworth.
With thy estimation - The wrong done or the defraud committed should be estimated at the number of shekels it was worth, or for which it would sell. These the defrauder was to pay down, to which he was to add a fifth part more, and bring a ram without blemish for a sin-offering besides. There is an obscurity in the text, but this seems to be its meaning.
Commit a trespass - Rather, here and in Leviticus 6:2, perpetrate a wrong. The word is different from that rendered trespass elsewhere in these chapters.
Through ignorance - Through inadvertence. See Leviticus 4:2 note.
In the holy things of the Lord - The reference is to a failure in the payment of firstfruits, tithes or fees of any kind connected with the public service of religion by which the sanctuary suffered loss; compare Numbers 5:6-8.
Shekel of the sanctuary - See Exodus 38:24 note.